(1-1/x)/(x^2-2x+1)/(x^2-1)=[(x-1)/x]/[(x+1)(x+1)]/[(x+1)(x-1)]=[(x-1)/x]/[(x+1)/(x-1)]=1/x/[(x+1)=1/[x(x+1)]=1/(2+根号2)=(2-根号2)/[(2+根号2)(2-根号2)]=(2-根号2)/2
